Driving means for high-speed printing apparatus



Oct. 22, 1968 M ss ET AL 3,406,625

DRIVING MEANS FOR HIGH-SPEED PRINTING APPARATUS Filed Aug. 25, 1967 5Sheets-Sheet 1 LELAND D. CHAMNESS ANDRE F. MARION PI 5 l INVENTOR.

ATRNE Oct. 22, 1968 L. D. CHAMNESS ET AL 3,406,525

DRIVING MEANS FOR HIGH-SPEED PRINTING APPARATUS Filed Aug. 25, 1967 3Sheets-Sheet 2 ENGAGE x DISENGAGE KEYBOARD- BUFFER DATA INPUT DELAY LINECOINCIDENCE PRINT CIRCUIT HAMMER TIMING SEQUENCE s2 MAGNETIC SENSINGHEADS 34, 36

FIEI I:

1.. D. CHAMNESS ET AL 3,406,625

DRIVING MEANS FOR HIGH-SPEED PRINTING APPARATUS Oct. 22, 1968 3Sheets-Sheet 5 Filed Aug. 25, 1967 United States Patent 0 3,406,625DRIVING MEANS FOR HIGH-SPEED PRINTING APPARATUS Leland D. Chamness,Castro Valley, and Andre F. Marion,

Berkeley, Calif., assignors to Friden, Inc., a corporation of DelawareContinuation-impart of application Ser. No. 528,501,

Feb. 18, 1966. This application Aug. 25, 1967, Ser.

14 Claims. (Cl. 101-93) ABSTRACT OF THE DISCLOSURE A printing carriageis cyclically driven by means of a rotatable shaft having a helical-likeshaped groove therein. One end of the groove has a variable pitchportion which is less than the pitch of the remainder of the groove anda ramp is located at the other end of the groove. A detent pin mountedto the carriage engages the variable pitch portion of the groove whichenables the carriage to be coupled to the groove shaft, while the shaftis rotating, and smoothly brought up to a constant velocity, from astart position, with printing enabled to take place during the constantvelocity travel of the carriage. To effect zero suppression and todecrease line-to-line printing time, the detent pin may be Withdrawnfrom the groove anywhere along the length thereof. However, if a fullline of printing is to take place, the ramp disengages the pin from therotating shaft, when the detent pin reaches the end of the groove,thereby disengaging the carriage from the shaft. When disengaged fromthe rotating shaft, the carriage is automatically returned to its startposition.

RELATED APPLICATION This application is a continuation-in-part of ourearlier filed application entitled, High Speed Printing Apparatus, Ser.No. 528,501, filed Feb. 18, 1966, now abandoned.

FIELD OF THE INVENTION This invention relates to a novel drive means,and in particular to a drive mechanism that is useful for transportingcarriages or supports, such as utilized in high-speed automatic printingapparatus.

Although this invention is applicable to driven devices generally, thefollowing description will be directed to highspeed printers for thepurpose of explanation.

DESCRIPTION OF THE PRIOR ART One class of high-speed printers employs aprint harnmer, a rotary disk or drum supporting a plurality ofcharacters on the periphery thereof, and a record medium or paper toreceive imprinting by the action between the character support and thehammer. The print hammer and/or the character support are transportedlinearly relative to the paper so that line printing may be elfectuated.For the print operational mode, uniform or constant speed drive isdesirable. Heretofore in the prior art, the back and forth movement ofthe printing carriage has been achieved by means of a rotatable element,such as a shaft. This is accomplished by coupling the carriage t0 theshaft while it is not rotating and then rotating the shaft to move thecarriage through the print mode. After printing takes place, thecarriage is decoupled from the shaft, returned to its start position andthe rotation of the drive shaft ceases to again enable coupling to thecarriage. This arrangernent has the disadvantage of the necessity ofstarting and stopping the rotation of the drive shaft for each printline and is not adapted to high speed line-to-line printing. Anotherarrangement is to have the printing carriage permanently coupled to thedrive shaft which enables the "ice drive shaft to be continuouslyrotated. This arrangement has the disadvantage that the print carriagetraverses a complete print line for each cycle. For example, a printline may include thirty or more character spaces, however, a particularprint line may require that information be printed in only one, or a fewof the available spaces. Regardless of the number of character spacesprinted, the carriage :must traverse the entire print line. Also, sincethe motion of the carriage must be reversed at the beginning and end ofeach print line, the velocity of the coupled carriage prior to havingits direction of motion reversed must be carefully controlled. A primaryobject of this invention is to overcome these and other disadvantages ofthe prior art.

SUMMARY OF THE INVENTION According to this invention, a high-speedautomatic printer apparatus comprises a rotary character wheel and printhammer means coupled to a common carriage, which is cyclically drivenalong successive print lines. The motion of the carriage is controlledby a continuously rotatable, channeled or contoured guide that enables,for each cycle or line of printing, acceleration from a start positionduring a first interval, then constant speed drive for line printingduring a second period, and disengagement of the carriage from the guideat an end-of-print position thereby allowing return to the startposition.

In a specific embodiment of this invention, the carriage is coupled to arotating shaft by a detent pin that follows a groove formed in theshaft. The groove consists of dis tinct portions; the first portionbeing a short straight slot fonmed in a plane substantially orthogonalto the axis of the shaft; a second portion providing a transition bymeans of a progressive spiral from the straight slot to a helical thirdportion having a constant pitch; and a fourth portion constituting aramp or incline which enables the pin, and therefore the carriage, to beautomatically disenvgaged from the shaft. Each portion serveseffectively to control the action and movement of the carriage. Also, inorder to effect zero suppression and to decrease lineto-line printingtime, disengagement of the carriage from the 'grooved, rotating shaftmay take place anywhere along the length thereof.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described ingreater detail with reference to the drawings in which:

FIG. 1 is a perspective view taken from the rear of the apparatus andshows the drive apparatus as used in a high-speed printer, in accordancewith the invention;

FIG. 2 is a fragmentary sectional view of a portion of the driveapparatus shown at the beginning of a print line cycle;

FIG. 3 is another fragmentary sectional view of the same portion of thedrive apparatus shown in FIG. 2 and shows the drive apparatus at the endof a print line cycle;

FIG. 4 is a simplified logic block diagram to aid in the explanation ofthe invention;

FIG. 5 illustrates a contoured drive shaft in accordance with thepresent invention;

FIG. 6 illustrates a modification of the apparatus shown in FIGS. 2 and3 and which enables Zero suppression; and

FIGS. 7 and 8 illustrate an end view and partial crosssection,respectively, of apparatus which activates the zero suppressionapparatus of FIG. 6.

Similar reference numerals refer to the same or similar elementsthroughout the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to FIG. 1, ahigh-speed automatic printer comprises a carriage 10 that is coupled toa rotary character wheel 12 and a print hammer assembly 14 forconjunctive travel and disposed in opposition, i.e., printing relation.The character wheel 12, which may be made of hard steel, aluminum, orplastic, by way of example, carries a multiplicity of helically arrangedraised characters or symbols to be printed on a record medium or paper16 that is fed by a transport means (not shown) between the characterwheel 12 and hammer assembly 14. The character wheel 12 is soconstructed and arranged that the characters thereon are helical inform. The wheel is mounted to a rotary shaft 18 that is driven through agear train (not shown) and a shaft 42 which is continuously rotatable bymeans of a drive motor (not shown) and a cog belt 20. The wheel 12 ispositioned on a squareshaped portion 24 of the shaft 18. A yoke (notshown) that is supported by a bracket portion 26 of the carriage drivesthe character wheel 12 along the axis of the shaft 18 as the carriage 10is moved back and forth cyclically. In this manner, the wheel 12 isadapted to achieve simultaneous rotary and linear motion relative to thefixed frame 74 of the apparatus.

Also mounted to the shaft 18 is a timing disk 28 formed from a magneticmaterial and having a plurality of circularly aligned apertures 30corresponding in number to the plurality of character positions on thewheel 12. In addition, an index or reference aperture 32 is located onthe magnetic disk 28 for indicating each complete revolution of the diskand to provide a reference thereby. The apertures 30 and 32, which inessence form nonmagnetic gaps, are detected, as they traverse theirrespective rotary paths, by magnetic sensing devices or heads 34 and 36,respectively, by virtue of changes in magnetic reluctance. Each sensedchange is converted to an electrical signal that is fed to a counter orlogic circuit, in which the instantaneous position of the disk 28, andthus the related angular position of the wheel 12, is registered. Themagnetic heads 34 and 36 are secured to an adjusting bracket 38 whichmay be rotated along a slot 40 whereby proper synchronization of thetiming signals relative to the character wheel is achieved. Othersensing means, such as systems utilizing optical radiation andphotosensitive cells, may be employed for determining the position orphase of the character wheel 12.

In accordance with this invention, a contoured, continuously rotating,cylindrical guide 42 (which is the main drive shaft) having a recessedconfiguration 44 is provided for controlling the forward motion of thecarriage 10. As shown in FIG. 5, one end of the recess 44 is a slottedportion 46 having a circumferential path substantially perpendicular tothe axis of the contoured cylindrical guide 42. The groove following theslot 46 varies angularly, increasing in pitch, and then assumes ahelical form 48 of substantially constant pitch. The length of thevariable pitch portion depends upon the mass of the carriage 10 and thespeed of the rotating shaft 42. At the end of such helical portion, thegroove becomes shallow to establish a ramp or cam 50 which is employedas a carriage disengaging means at the end of each printing cycle, aswill be described hereinafter.

Referring again to FIG. 1, a small permanent magnet 52 is fixed to oneend of the rotating cylindrical guide 42 relative to the slotted portion46 of the helical groove 48 and provides an indication of the angularHome position or phase of the rotating guide cylinder 42, suchindication being utilized at the start of each line print cycle. As theguide cylinder 42 rotates, the magnet 52 periodically passes adjacent toa reed switch S1. The switch S1 is closed by the proximity of the magnetand energizes 'a circuit, which establishes that the guide cylinder 42is in its angular Home position. The angular Home position or phaserepresents a predetermined rotary position of the guide 42 at which timethe detent pin 58 can readily engage the grooved start portion 46.

At the beginning of each line print cycle, when the guide 42 is sensedas being in the angular Home phase,

4 a a striking hammer 54 is actuated by means of an electromagnet 56,that is energized by circuit means coupled to the reed switch S1. Thehammer 54 depresses a detent pin 58, shown in detail in FIG. 2, so thatthe pin is locked in engagement with the slotted start portions 46 ofthe continuous recess 44 in the guide 42. The pin 58 remains seated inthe slot 46 and in the following angular recessed portions of the guideby means of a common spring ball detent 60.

The pin 58 is secured by a support 62 that forms part of the movablecarriage 10. Therefore, as the pin 58 is urged in the axial direction ofthe guide 42, then the support 62 and carriage 10 are also propelledaxially. Similarly, the character Wheel 12 which is coupled to thecarriage 10 is moved along the axis of the shaft 18, that is,substantially parallel to the guide 42. Due to the configuration of thestart portion 46 of the groove 44, the carriage 10 can engage the shaft42, even though it is rapidly rotating, and be smoothly and evenlybrought up to a constant velocity at which time line printing occurs.

When the carriage 10 is in the axial Home" position, i.e., the positionat which the printing mode is to begin, this condition is sensed by apermanent magnet 64 that is adjustably secured to a predeterminedlocation on the carriage 10. The magnet 64 serves to energize a reedswitch S2 to provide an electrical signal that marks the beginning ofthe print mode portion of the print line cycle. The position of thescrew-mounted magnet 64 is adjustable, thus enabling the setting of theaxial Home position which, in turn, establishes the margin on the paper16 at which printing begins.

As the pin 58 is moved by the rotating grooved 44 shaft into the angularrecessed or helical portion 48, the carriage 10 bearing the magnet 64travels axially and is evenly accelerated during a start-up interval, inaccordance with the increasing pitch of the recess immediately followingthe straight slot 46. When the pin 58 reaches the beginning of theuniform pitch helical portion 48, the print mode is initiated. As thecarriage 10 moves away from the axial Home position, the magnet 64leaves the reed switch S2, thereby de-energizing the switch and breakingthe circuit. This action allows the print hammer 14 to be actuated forstriking whenever the character wheel 12 is in proper phase and incoincidence wit-h the character information from the data input circuit.As represented in the logic block diagram of FIG. 4, the data inputsignal is stored in a buffer, such as a delay line, and this signal, inconjunction with a counter signal developed by the magnetic sensing head34 referenced to the signal from the head 36, triggers a coincidencecircuit.

Thus it is seen that the print mode corresponds in time with the passageof the pin 58 across the constant pitch portion 48 of the guiding helixduring which time the carriage 10 is transported uniformly in a forwarddirection. Before actual printing commences, the following sequence ofevents occurs, as illustrated in FIG. 4:

(l) The helically grooved shaft 42 is rotating.

(2) The angular Home phase of the guide 42 is detected, the pin 58engages the slot 46 and the carriage moves from its start position.

(3) The axial Home position of the carriage 10 is sensed.

(4) After a predetermined delay, the magnetic sensors determine that thecharacter wheel 12 is in position to print the character correspondingto that received from the data input and stored in the buffer.

During operation, after the printer apparatus has been switched on, thefirst character or numeral is introduced to the data input system, forexample, by depression of a key of a keyboard associated with theprinter. The data signals representing characters may also be derivedfrom a record tape or some other suitable storage medium.

During the printing period, an electromagnet 15 is energized by a pulsesignal received from the coincidence circuit or gate, which is actuatedwhen the character input conforms with the character position of thewheellZ,

The electromagnet 15 operates the hammer of the hammer assembly 14 whichetfectuates an imprint of the selected character on the paper 16 that isdisposed in the interstice between the print wheel and hammer.

The length and the pitch of the uniform helical portion 48 is such thatthe time of travel of the carriage along the constant pitch portioncorresponds in time to a line period of printing of data. At the end ofsuch print mode, the pin 58 reaches the end of the helical groove orspiral recess 44, and is disengaged by ejection caused by the action ofthe incline or ramp 50 on the pin, as depicted in FIG. 3. The detentball assembly 60 is released whereas a second spring ball detentassembly 66 becomes effective to retain the pin 58 in a retractedposition, thereby precluding engagement of the pin with the helicalgroove 48 of the contoured guide 42 as the carriage is returned to itsstart position.

Upon disengagement of the pin from the guide, the carriage isautomatically urged to return to the start position by a resilient meansor spring 68, which was compressed during the forward travel of thecarriage. The spring 68 exerts decompression force against a carriageextension bracket 70 to achieve a relatively fast return of thecarriage. A dashpot 72 damps the fast return motion of the carriage, ina well-known manner, as the carriage 10 approaches the start position.As the carriage reaches its start position, the magnet 64 closes theswitch S2 so that no printing can take place until constant forwardspeed of the carriage is again realized and the magnet 64 has againpassed the switch S2 to signify the start of the print mode. Thus,successive lines of data may be imprinted at high speeds under controlof a sculptured or contoured guide coupled to a carriage that carriesboth the print hammer and print wheel in cooperative relation withoutthe necessity of stopping and starting the rotation of the shaft 42between print lines. However, it is to be understood that for those timeintervals during which no printing occurs, the shaft 42 need not berotating.

For ease of explanation, the circuitry and circuit connections have notbeen shown or described in detail. It is understood that it iswell-known to those skilled in the art to provide the signals and pulsesfor firing the print hammer 14 and pin striking hammer 54 whennecessary.

In the apparatus described above, the carriage 10 is driven the entirelength of the groove 44 and is disengaged by the ramp 50. In order toeffect zero suppression and to decrease line-to-line printing time, itis desirable to disengage the carriage 10 from the grooved 44 shaft 42as soon as the last character in each print line has been printed. Thiscan be accomplished, as shown in FIG. 6, by a rotatable shaft 81 whichpasses through an opening 80 in the support 62. The detent pin 58 has areduced cross-sectional area intermediate its detents such that itpresents a flatted surface 83 adjacent a flatted surface 82 of the shaft81 as shown in FIG. 6. Once the last character of a print line has beenprinted, and if this occurs prior to the carriage 10 reaching the end ofthe groove 44 adjacent the ramp 50, clockwise rotation of the shaft 81will cause the detent pin, and therefore the carriage 10, to bedisengaged from the grooved 44 shaft 42 to automatically return thecarriage 10 to its start position, from which it can again be coupled tothe start portion 46 of the groove 44 in the rotating shaft 42.

Mechanism for so actuating the shaft 81 is illustrated in FIGS. 7 and 8which show a spring clutch 85 located adjacent the end of the groovedshaft 42 remote from the switch S1 (FIG. 1). The clutch 85 enables theshaft 42 to rotate a cam 97 which in turn actuates a cam follower 100which in turn rotates the shaft 81 in a clockwise direction by means ofa gear 103. The clutch 85 can be actuated by means of an electromagnet(not shown) which in turn is actuated by an electrical signal thatindicates the last character of the print line has occurred. Thiselectrical signal may be generated by any number of wellknown means thatprovide zero suppression for printers.

The operation of the apparatus shown in FIGS. 6, 7 and 8 is described indetail hereinbelow.

Following the engagement of the carriage drive pin 58 with the helicalgroove 44 of the rotating shaft 42, energization of the electromganet 15operates the print hammer 14 for the printing of a desired characterwith each revolution of the type wheel 12. As the printing of each digittype character is effected, a zero suppression circuit of a conventionaltype comes into play to sense all higher orders of the factor to beprinted. If the highest significant digit has been printed, the zerosuppression circuit effects engagement of the clutch (FIG. 8) by anysuitable means, such as an electromagnet (not shown). Upon engagement ofthe clutch 85, one revolution of a pinion gear 95 at a 72 angularrotation of the cam disk 97 causes the cam follower 100 to rock theshaft 81 clockwise (FIGS. 6 and 7) against the urgency of a spring (notshown), thereby withdrawing carriage drive pin 58 and releasing thecarriage 10 to the influence of the spring 68 which causes the carriage10 to automatically return to its start position.

Accordingly, upon completion of less than a full line of printedcharacters, whether it be one character or a plurality of characters,the carriage drive pin 58 is Withdrawn from its engagement with thegroove 44 of the continuously rotating shaft 42 to enable the automaticreturn of the carriage 10 and type-wheel 12 to the start position. Morespecifically, a capstan spring clutch 85 (FIGS. 7 and 8) is provided. Atits left end, as viewed in FIG. 8, the grooved 44 shaft 42 is supportedfor rotation within a cup-shaped bushing 86 which, in turn, isjournalled in a bearing bushing 87 secured in a side-frame member 84.Intermediate its ends, the bushing 86 is provided with an integrallyformed annular stepped flange 89 and disposed between the flange 89 andthe bearing bushing 87 is a spacing ring, or washer, 88. The internaldiameter of the cupshaped bushing 86 is sufiiciently greater than thediameter of the shaft 42 to provide a close running fit between theshaft and the bushing. The end surface of the openend portion of thebushing 86 abuts the end surface of the hub of a stepped collar 90secured on shaft 42 for rotation therewith. The outside diameter of thehub of the collar 90 and that of the abutting open-end portion of thebushing 86 is identical. Encircling the open-end portion of the bushing86, as well as the hub of the collar 90, is a tightly coiled spring 94having an inside diameter slightly less than the outside diameter of thetwo mating members. The diameter of the reduced portion or shoulder ofeach of the flanges 89 and 91 is identical and provides a bearingsurface for the respective ends of a sleeve 92, the inside diameter ofwhich is sufficiently greater than the outside diameter of the spring 94to permit expansion of the spring within the sleeve. One end of thespring 94 is anchored in a suitable notch in the flange 89 of thebushing 86, while the other end projects radially outwardly and isengaged in a suitable aperture in the sleeve 92, so that if the sleeve92 is held against rotation and shaft 42 is rotating in a clockwisedirection, as viewed from the left in FIG. 8, the spring 94 is expandedto provide a free running fit between the spring and the shaft 42.However, when the sleeve 92 is released, spring 94 is permitted toassume its normal form, thereby providing a drive connection betweenshaft 42 and the bushing 86.

Normally, the sleeve 92 is latched in the position shown in FIG. 8 todisable the driving function of the coil spriig 94. At the completion ofeach cycle of clockwise rotation of the clutch 85, i.e., after onerevolution of the sleeve 92, the upturned end portion of latch lever 93engages in an aperture (not shown) in the sleeve 92. Latch lever 93 ispreferably rockably mounted intermediate its ends. Secured on the closedend surface of the bushing 86 is a fourteen tooth pinion 95 concentricwith shaft 42, and enmeshed with the teeth of a seventy tooth internal 7gear .98 (FIGS. 7 and 8) of cam disk 97 rotatably mounted on pin 96secured on side frame member 84.

Upon energization of the clutch 70, a 72 angular rotation is imparted tothe cam disk 97. During this partial revolution of the cam disk 97, thecam follower 100 is rocked counter-clockwise about its pivot 101 on sideframe member 84. The cam follower 100 is provided with a toothed sector102, which is meshed with a pinion 103 secured on the end portion of theshaft 81 journalled in side frame member 84. In addition tobeingjournalled, shaft 81 also passes through the aperture 80 in the printhammer carriage support 62 (FIG. 6) and is normally resiliently urged bya spring (not shown) to the counterclockwise rocked position shown tomaintain the follower 100 in engagement with the peripheral surface ofcam disk 97. As the shaft 81 is rocked clockwise (FIGS. 6 and 7) by camfollower 100, the surface 82 of the flatted portion of the shaft 81engages the shoulder 83 formed in the carriage drive pin 58, moving thepin to the left out of engagement with the groove 44 on the shaft 42.Upon retraction of the carriage drive pin 58 from ts engagement with thegroove 44, the print hammer carriage 10 is released to the influence ofthe relatively strong spring 68 (FIG. 1) that returns the carriage toits start position.

It should be understood that the invention is not limited to theparticular configuration set forth above, but may employ alternativeembodiments. For example, the recessed guide may have a raisedconfiguration engaging a seating element. The configuration can bemodified to afford variations in speed of movement of the carriage.Also, the paper may be moved axially, and different approaches toachieve relative motion between the printing elements may be utilized.Furthermore, a plurality of hammers, or a plurality of character wheels,or different forms of character supports may also be utilized within thescope of the present invention. In addition, the drive mechanismdelineated herein is not necessarily limited to a high-speed printer,but may also find utility in various other apparatuses.

What is claimed is:

1. A drive apparatus comprising:

a movable carriage having at least a start position;

a rotatable, contoured element for controlling the motion of saidcarriage;

said contour having a start portion, an end portion,

and a major portion therebetween being formed as a substantially helicalgroove along said rotatable element; means for coupling said carriage tosaid start portion of said contoured element while said contouredelement is rotating to impart motion to said carriage;

means different from said means for coupling for disengaging saidcarriage from said contoured element while said contoured element isrotating; and

means for automatically returning said carriage to said start positionafter disengaging said carriage from said contoured element, said startportion of said groove including a first portion which is acircumferential slot in a plane substantially perpendicular to the axisof said contoured element and a second portion providing a transition bymeans of a progressive spiral from said slot to said helical portion.

2. The apparatus of claim 1 wherein said start portion of said contourhas a pitch less than that of said helical groove.

3. The apparatus of claim 1 wherein said start portion of said contourincludes a variably pitched, helical-like groove.

4. The apparatus of claim 1 wherein said coupling means includes adetent pin adapted to be seated in said contour.

5. The apparatus of claim 1 wherein said disengaging means includes aramp formed at the end portion of said contour.

6. The apparatus of claim 4 wherein said disengaging means includesmeans for withdrawing said detent. pin from. said contour anywhere alongthe length-thereofj 7. Theapparatus of claim 1 wherein said automaticcarriage returning means .includes resilient means coupled tosaidcarriage, said resilient means being'tensed when said carriageispropelled from said start position sotliat upon disengagement of saidcarriage from saidjcpntoured element said'resilient means urges saidcarriag'ejback to said start position. v I p v 8. A high speed printerapparatus comprising:

a rotary character wheel;

aprint hammer; V

a movable carriage, having a start position fo'r transporting said wheeland said print 'hainmer alongfja predetermined path in print relation ata substantially constant velocity; C v p a grooved, rotatable shaftdisposed along such predetermined path; V p, p v

said groove having a start portion, an end portion, and a major portiontherebetween being'a substan- Y tially helical groove around said shaft;

means for coupling said carriage tosaid start portion of said groovewhile said shaft is 'rot-atingwhereby 'motion is imparted .to saidcarriage along said predetermined path; p

said start portion of said grove adapted to evenly accelerate saidcarriage from said start position, said start portion of said grooveincluding a first portion which is a circumferential slot in a planesubstantially perpendicular to the axis of said contoured element and asecond portion providing a transition by means of a progressive spiralfrom said slot tosaid helical portion; said major portion of said grooveadapted to impart a substantially constant velocity to said carriage du'ring which time printing may occur; r p means different from saidmeansforcoupling, forjdisiengaging said carriage from said groovedshaft; and means for automatically returning said carriage to said startposition after disengaging said carriage from said grooved shaft. I p

9. The apparatus of claim 8 wherein said groovedstart portion has apitch less than that of said grooved major portion. v v

10. The apparatus of claim 9 wherein said grooved start portion has avariable pitch. A

11. The apparatus of claim 10 wherein said coupling means includes adetent pin adapted to engage said groove.

12. The apparatus of claim 11 wherein said disengaging means includes aramp formed at the end portion of said groove.

13. The apparatus of claim 11 wherein said disengaging means is adaptedto withdraw said detent pin from said groove anywhere along the lengththereof. v

14. The apparatus of claim 11 wherein said automatic returning meansincludes resilient means coupled to said movable carriage, saidresilient means being tensed when said carriage is propelled along saidpredetermined path whereby said resilient means urges said carriage backto said start position upon disengagement of said carriage from saidgrooved shaft.

References Cited UNITED STATES PATENTS 2,604,788 7/1952 Hauber 74-12,805,620 9/1957 Rosen et al. 101-93 2,843,243 7/1958 Masterson 101- 93XR 3,080,765 3/1963 Eisele 74-57 3,151,547 10/1964 Hornauer et al.101-93 XR 3,154,672 10/1964 Larkin 235-92 3,167,166 1/1965 Schiebeler197-1 3,232,404 2/1966 Jones 101-93 XR ROBERT E. PULFREY, PrimaryExaminer. E. S. BURR, Assistant Examiner.

